Fix handling of TERM signal to exit borgmatic, not just forward the signal to Borg (#516).

borgmatic/signals.py

@@ -1,23 +1,34 @@
+import logging
 import os
 import signal
+import sys
+
+logger = logging.getLogger(__name__)
 
 
-def _handle_signal(signal_number, frame):  # pragma: no cover
+EXIT_CODE_FROM_SIGNAL = 128
+
+
+def handle_signal(signal_number, frame):
     '''
     Send the signal to all processes in borgmatic's process group, which includes child processes.
     '''
     # Prevent infinite signal handler recursion. If the parent frame is this very same handler
     # function, we know we're recursing.
-    if frame.f_back.f_code.co_name == _handle_signal.__name__:
+    if frame.f_back.f_code.co_name == handle_signal.__name__:
         return
 
     os.killpg(os.getpgrp(), signal_number)
 
+    if signal_number == signal.SIGTERM:
+        logger.critical('Exiting due to TERM signal')
+        sys.exit(EXIT_CODE_FROM_SIGNAL + signal.SIGTERM)
 
-def configure_signals():  # pragma: no cover
+
+def configure_signals():
     '''
     Configure borgmatic's signal handlers to pass relevant signals through to any child processes
     like Borg. Note that SIGINT gets passed through even without these changes.
     '''
     for signal_number in (signal.SIGHUP, signal.SIGTERM, signal.SIGUSR1, signal.SIGUSR2):
-        signal.signal(signal_number, _handle_signal)
+        signal.signal(signal_number, handle_signal)